Introduction:
Two main types of bearing are used in rear wheel hubs: ball and roller (or tapered roller) bearings.
Axle shafts:
Axle shafts transmit drive from the differential to the rear wheel hubs. An axle shaft has to withstand:
● Torsional stress due to driving and braking forces
● Shear and bending stress due to the weight of the vehicle
● Tensile and compressive stress due to cornering forces
A number of bearing layouts are used on the fixed live axle (driven) of a rear wheel drive car, to handle these stresses.
Wheel bearing: semi-floating:
Wheel bearing: three-quarter floating
The three-quarter floating bearing reduces the main shear stresses on the axle shaft but the other stresses remain. The bearing is mounted on the outside of the axle tube. An oil seal is included to prevent the brake linings from being contaminated.
Wheel bearing: fully floating
Front hub (rear-wheel drive) with tapered roller bearings
The front hubs on rear-wheel drive cars consist of two bearings. These are either ball or tapered roller. The roller types are generally used on earlier vehicles. They have to be adjusted by tightening the hub nut and then backing it off by about half a turn.
Front hub with ball bearings
The more modern hub bearings, known as contact-type ball races, do not need adjusting. This is because the hub nut tightens against a rigid spacer. This nut must always be set at a torque specified by the manufacturer.